Buggy code:
public class LoginActivity extends Activity { Button loginbutton ; Button signup ; String usernametxt ; String passwordtxt ; EditText password ; EditText username ; public void onCreate ( Bundle savedInstanceState ) { super . onCreate ( savedInstanceState ) ; Parse . initialize ( this , "pizEYCj8zYu8dcQ9AU7DxfRqGjx6Lt9Ie2aHV8Rn" , "5e9eoQeZiL8yKntAe9tRmRsp3Xe7l9fLShGwoz7E" ) ; setContentView ( activity_login ) ; username = ( ( EditText ) ( findViewById ( R . id . username ) ) ) ; password = ( ( EditText ) ( findViewById ( R . id . password ) ) ) ; loginbutton = ( ( Button ) ( findViewById ( login ) ) ) ; signup = ( ( Button ) ( findViewById ( R . id . signup ) ) ) ; loginbutton . setOnClickListener ( new OnClickListener ( ) { public void onClick ( View arg0 ) { if ( isNetworkConnected ( ) ) { usernametxt = username . getText ( ) . toString ( ) ; passwordtxt = password . getText ( ) . toString ( ) ; ParseUser . logInInBackground ( usernametxt , passwordtxt , new LogInCallback ( ) { public void done ( ParseUser user , ParseException e ) { if ( user != null ) { Intent intent = new Intent ( LoginActivity . this , HomeActivity . class ) ; startActivity ( intent ) ; Toast . makeText ( getApplicationContext ( ) , "Successfully<seq2seq4repair_space>Logged<seq2seq4repair_space>in" , LENGTH_LONG ) . show ( ) ; finish ( ) ; } else { Toast . makeText ( getApplicationContext ( ) , "No<seq2seq4repair_space>such<seq2seq4repair_space>user<seq2seq4repair_space>exist,<seq2seq4repair_space>please<seq2seq4repair_space>signup" , LENGTH_LONG ) . show ( ) ; } } } ) ; } else { Toast . makeText ( getApplicationContext ( ) , "Device<seq2seq4repair_space>is<seq2seq4repair_space>not<seq2seq4repair_space>connected<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space>internet.<seq2seq4repair_space>You<seq2seq4repair_space>cannot<seq2seq4repair_space>log<seq2seq4repair_space>in." , LENGTH_LONG ) . show ( ) ; } } } ) ; signup . setOnClickListener ( new OnClickListener ( ) { public void onClick ( View arg0 ) { if ( isNetworkConnected ( ) ) { usernametxt = username . getText ( ) . toString ( ) ; passwordtxt = password . getText ( ) . toString ( ) ; <START_BUG> if ( ( usernametxt . equals ( "" ) ) && ( passwordtxt . equals ( "" ) ) ) { <END_BUG> Toast . makeText ( getApplicationContext ( ) , "Please<seq2seq4repair_space>complete<seq2seq4repair_space>the<seq2seq4repair_space>sign<seq2seq4repair_space>up<seq2seq4repair_space>form" , LENGTH_LONG ) . show ( ) ; } else { ParseUser user = new ParseUser ( ) ; user . setUsername ( usernametxt ) ; user . setPassword ( passwordtxt ) ; user . signUpInBackground ( new SignUpCallback ( ) { public void done ( ParseException e ) { if ( e == null ) { Toast . makeText ( getApplicationContext ( ) , "Successfully<seq2seq4repair_space>Signed<seq2seq4repair_space>up,<seq2seq4repair_space>please<seq2seq4repair_space>log<seq2seq4repair_space>in." , LENGTH_LONG ) . show ( ) ; } else { Toast . makeText ( getApplicationContext ( ) , "Sign<seq2seq4repair_space>up<seq2seq4repair_space>Error" , LENGTH_LONG ) . show ( ) ; } } } ) ; } } else { Toast . makeText ( getApplicationContext ( ) , "Device<seq2seq4repair_space>is<seq2seq4repair_space>not<seq2seq4repair_space>connected<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space>internet.<seq2seq4repair_space>You<seq2seq4repair_space>cannot<seq2seq4repair_space>log<seq2seq4repair_space>in." , LENGTH_LONG ) . show ( ) ; } } } ) ; } private boolean isNetworkConnected ( ) { } }

Fix:
if ( ( usernametxt . equals ( "" ) ) || ( passwordtxt . equals ( "" ) ) ) {